Refining of molten iron

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR THE REFINING OR TREATMENT OF METALS AND HAS PARTICULAR REFERENCE TO THE PRODUCTION OF STEEL IN AN OPEN HEARTH FURNACE OR IN A TOP BLOWN CONVERTER BY SUBJECTING A MELT OF THE STEEL TO AN OXYGEN TREATMENT IN A REFINING VESSEL BY INJECTING INTO THE VESSEL A FLAME FED BY STREAMS OF OXYGEN AND LIQUID CARBONACEOUS FUEL AND ADJUSTING THE PROPORTIONS OF OXYGEN TO FUEL TO OBTAIN SUBSTANTIALLY COMPLETE COMBUSTION AND LOCATING THE FLAME WITHIN THE VESSEL SO THAT THE FLAME DOES NOT IMPINGE UPON THE MELT.

United States Patent 3,583,865 REFINING 0F MOLTEN IRON Hugh W. Grentell, Port Talbot, South Wales, assignor to The Steel Company of Wales Limited, Port Talbot, Glamorgan, South Wales No Drawing. Filed Feb. 13, 1967, Ser. No. 615,310 Claims priority, application Great Britain, Feb. 16, 1966, 6,847/ 66 Int. Cl. C21c 5/28 US. Cl. 75--60 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the refining or treatment of metals and has particular reference to the production of steel in an open hearth furnace or in a top blown converter by subjecting a melt of the steel to an oxygen treatment in a refining vessel by injecting into the vessel a flame fed by streams of oxygen and liquid carbonaceous fuel and adjusting the proportions of oxygen to fuel to obtain substantially complete combustion and locating the flame within the vessel so that the flame does not impinge upon the melt.

The disclosure of US. Pat. No. 3,313,535, filed Jan. 25, 1965, and assigned to the same assignee of the present invention is incorporated herein.

The present invention relates to the refining or treatment of molten metals, and has particular reference to an improved process for the refining of steel in an L.D. or B.O.F. converter or in an open hearth furnace.

According to the present invention, there is provided a process for the refining or treatment of metals which process includes the step of subjecting a melt of the metal to an oxygen treatment within a refining vessel until the refining or treatment is complete, by injecting into the vessel a flame fed by streams of oxygen and liquid carbonaceous fuel, adjusting the proportions of oxygen to fuel to obtain substantially complete combustion and locating the flame within the vessel so that the products of combustion but not the flame impinge upon the melt.

The present invention also provides for the production of steel in an open hearth furnace or in a top blown converter, which process comprises injecting into the vessel, a flame fed by streams of oxygen and liquid carbonaceous fuel until the refining is completed, adjusting the proportions of oxygen to fuel to obtain substantially complete ombustion and locating the flame within the vessel so that the products of combustion but not the flame impinge upon the melt.

It is preferred that there is an excess of oxygen over the quantity of oxygen required to effect complete combution of the fuel and the excess may be greater than 1,000 percent of that required to obtain complete combustion of the fuel. Alternatively, the excess of oxygen may typically be within the range 150 and 200 percent.

The liquid carbonaceous fuel may be a hydrocarbon fuel oil or a coke oven tar of low sulphur content and the streams of oxygen and liquid fuel may be injected into the refining vessel by means of a multi-jet blowing nozzle such as that forming the subject of complete specification No. 1,021,099. It is desirable that during the refining reaction, the flame should not impinge upon the melt in order to reduce contamination of the melt by the introduction of sulphur.

The oxygen may be preheated in the nozzle or in the flame since it will be appreciated that in the process, using a conventional top blown converter, as hitherto employed, the oxygen used hitherto is cold and in fact will Patented June 8, 1971 be further cooled by the adiabatic expansion which takes place when the oxygen is emitted from the nozzle and this constitutes a considerable drain on the heat produced in the reactions of the process and thus limits the quantity of any scrap which may be charged to the melt prior to or during the refining process.

In a conventional top blown converter, the oxygen required for refining a ferrous charge to steel is, for example 2,000 cubic foot per ton of steel produced. The process of the present invention results in the production of an extremely hot flame which enables the temperature of the charge in the converter to be controlled during the reaction by, if necessary, varying the proportions of fuel to oxygen in the mixture. The present invention permits a considerably larger proportion of scrap to be used as calculated from the heat of the combustion of the quantity of the fuel oil and the heat required to raise the scrap to tapping temperature. However, the scrap addition must be calculated having regard to the need to maintain a careful heat balance during the process.

It has been found that by using the process of the present invention, a considerable reduction in the fume results during steel making and consequently such use may reduce the level of fume to that acceptable by the health authorities.

The fuel oxygen mixture may be injected into the refining vessel by means of a multi-jet blowing nozzle which may be incorporated at the end of a blowing lance, such as that described and claimed in our complete specification Ser. No. 1,021,099, which comprises an elongate body member having a fuel supply conduit centrally located therein, and an oxygen supply conduit surrounding said fuel supply conduit to provide an annular passageway for the supply of oxygen wherein the body member is provided with a delivery nozzle at one end thereof formed with a plurality of discharge orifices and communicating with said oxygen supply conduit through a plurality of oxygen supply pipes disposed at an angle to the longitudinal axis of the lance and wherein the fuel supply conduit is provided at its outlet end with a plurality of fuel supply pipes extending therefrom and each having its end portion situated in a corresponding oxygen supply pipe so that oxygen flowing through said supply pipes to the discharge orifices will flow in an annulus around the end of the corresponding fuel supply pipes whereby fuel will be entrained in the oxygen supplies when discharged from the discharge orifices.

Some modification of the lance, is, however, necessary in order to adapt such a lance for use with an L.D. or B.O.F. steel making apparatus. The length of the lance is substantially increased and consequently there is the possibility of excessive cooling of the fuel oil due to its travel down the lance. This cooling may be prevented by lagging the fuel oil supply pipe or by providing an additional pipe outside the fuel supply pipe leaving a gap so as to provide a resistance to heat transfer.

In use, with an open top blown converter, the lance is located towards the open top of the converter and the oxygen and fuel oil supply to the lance is turned on. The mixture ignites at the nozzle outlet to provide a flame extending some 1.5 ft. to 2, ft. from the discharge orifices in the end of the lance. The lance is then lowered so that the discharge orifices are within 4 to 6 ft. from the surface of the melt, that is to say, so that the flame per se does not impinge upon the melt surface. The supply of the oxygen/ fuel oil mixture is continued until the refining operation is complete. It is noted that there is a considerable reduction of the fume produced during the operation and it is possible to make a visual observation of the material within the refining vessel.

In a typical example of the process of the present invention, a refining vessel of 135 tons capacity was charged as follows:

Tons Scrap steel 45.4 Hot metal 89.57 Cold pig iron 2.45

The hot metal was molten pig iron at a temperature of 1400 C.; the hot metal and cold pig iron have the same analysis, namely as follows:

Percent by weigh Carbon 4.2 Silicon 0.65 Manganese 0.75 Phosphorus 0.15 Sulphur 0.025

the balance apart from incidental impurities being of iron.

A blowing lance, having a construction as specifically disclosed in complete specification No. 1,021,099 was located with the discharge nozzles just within the top of the vessel and spaced some 16 ft. from the surface of the melt within the vessel. Oxygen was supplied to the lance to issue from the discharge orifices at the rate of 10,000 cu. ft. per minute and a hydrocarbon fuel oil was supplied to the lance at a rate of 400 gallons per hour. The mixture on debouching from the discharge orifices was ignited to produce a flame substantially 1.5 ft. in length. After ignition the lance was lowered towards the surface of the melt until the discharge orifices were approximately ft. from the surface of the melt. The oxygen/fuel oil blow was continued throughout the period of the reaction, that is to say, for approximately 20 minutes and during the reaction 4.2 tons of mill scale comprising substantially Fe O with a small proportion of Fe O was added together with 4.57 tons of lime and 0.31 tons of fluorspar to flux the slag. During the course of the reaction it was noted that little fume was produced and it was possible to observe the surface of the melt during the reaction.

When the reaction was complete, the supply of oxygen and fuel oil was terminated and the molten steel was tapped from the vessel.

It was found that the steel produced in this way was of good quality and had a low sulphur content.

I claim:

1. A process for refining molten iron by subjecting a melt to refining gases comprising:

(A) creating a flame in a converter vessel and preventing said flame from impinging the melt;

(B) feeding said flame with a stream of oxygen and liquid carbonaceous fuel, said oxygen being in an amount at least sufficient to obtain complete combustion of the liquid fuel; and

(C) impinging any uncombined oxygen and products of combustion upon said melt until refining is complete.

2. A process as set forth in claim 1 wherein a plurality of flames are created and fed by a plurality of associated streams of oxygen and carbonaceous liquid fuel.

3. A process as set forth in claim 1 wherein said oxygen is fed in an amount in excess of that required for the complete combustion of the fuel.

4. A process as set forth in claim 1 wherein the liquid carbonaceous fuel is selected from the group consisting of a hydrocarbon fuel oil and coke oven tar.

5. A process as set forth in claim 1 where said oxygen stream is fed as an annular sheath around said stream of liquid carbonaceous fuel to isolate said flame from the melt by an annular sheath of oxygen and combustion products.

6. A process as set forth in claim 2 wherein said oxygen streams each form an annular sheath about an associated stream of liquid carbonaceous fuel.

References Cited UNITED STATES PATENTS 3,313,535 4/1967 Hopkins 26634.1 3,130,252 4/1964 Metz 60X 3,141,763 7/1964 Foresi et al 7560 3,115,405 12/1963 Boyd 7560X 3,138,452 6/1964 Aihara et al 7560 3,234,011 2/1966 Rinesch 7560 3,323,907 6/1967 Kurzinski 7560 FOREIGN PATENTS 6,411,376 4/1965 Netherlands 7560 1,453,442 8/1965 France 75-60' L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner 

